Passive feed networks have been known to be combined with discrete-element antenna arrays. These known antenna arrays typically have dipole or patch radiating elements. By providing a progressive, constant-difference phase shift to the point-source radiating elements, a beam pattern produced by the antenna may be steered from perpendicular with respect to the antenna face.
Such known steerable arrays typically have from 5-15 discrete radiating elements. Some antenna arrays may have more radiating elements. However, the dipole or patch radiating elements are discrete radiating elements. They are typically driven separately, and operate as point sources. Additionally, the dipole or patch radiating elements generate an electromagnetic field by surface current.
Another type of antenna comprises a strip of dielectric with a series of polarization devices. Each polarization device may comprise, for example, a pair of electrodes separated by the dielectric. As the electrodes are driven, a displacement current occurs in the dielectric. This displacement (or volume polarization) current within the dielectric radiates an electromagnetic field. Thus, this type of element is considered a volume polarization source of electromagnetic radiation. The volume polarization current distribution may be caused to propagate by appropriate sequencing of the energization of the polarization devices. Known volume source arrays have elements that are driven by individual amplifiers. See, for example, U.S. Pat. No. 8,125,385, which is incorporated by reference.
Volume polarization current sources of electromagnetic radiation whose distribution patterns move faster than light in vacuum have been experimentally realized. One example of a superluminal source that has already been constructed and tested functions by producing a polarization current with a rotating distribution pattern in a ring-shaped dielectric (such as alumina); by a phase-controlled excitation of voltages applied to electrodes that surround the dielectric, the polarization pattern can be set in motion with superluminal speed and centripetal acceleration. See, e.g., U.S. Pat. Pub. No. 2006/0192504; see also, U.S. application Ser. No. 13/368,200, titled “Superluminal Antenna” and filed on Feb. 7, 2012, the disclosures of which are incorporated by reference. These devices produce tightly-focused packets of electromagnetic radiation fundamentally different from the emissions of conventional sources.
Once a source travels faster than light with acceleration, it can make contributions at multiple retarded times to a signal received instantaneously at a distance. For those volume elements of an extended source that approach the observation point, along the radiation direction, with the speed of light and zero acceleration, these multiple contributions coalesce and give rise to a focusing of the received waves in the time domain: the interval of observation time during which a particular set of wave fronts is received is considerably shorter than the interval of retarded time during which the same set of waves is emitted by such source elements. As a result, part of the emitted radiation possesses an intensity that decays nonspherically with the distance d from the source: as 1/d rather than as the conventional inverse square law, 1/d2. This does not contravene the conservation of energy. The constructively interfering waves from the particular set of elements responsible for the nonspherically decaying signal at a given observation point constitute a beam that narrows with distance. The area subtended by the beam increases as d, rather than d2, so that the flux of energy remains the same across all cross sections of the beam. In that it consists of caustics and so is constantly dispersed and reconstructed out of other waves, the beam in question is, of course, radically different from a conventional radiation beam.
Another example of a superluminal source is one for which the polarization distribution pattern moves rectilinearly. In one example, the polarization distribution pattern moves with an acceleration that increases linearly with its displacement from a negative to a positive value. When its speed exceeds the speed of light in vacuo on the plane where its acceleration vanishes, this source, too, generates an emission whose intensity diminishes as 1/d. The morphology of the nonspherically decaying radiation beam generated by the present source is very different from that of the radiation beam that is generated by a centripetally accelerated superluminal source. While the beam generated by a rotating superluminal source consists of a collection of nondiffracting subbeams that are observable over a wide solid angle, in the present case, the nonspherically decaying component of the radiation propagates into a narrowing beam at a fixed angle relative to the direction of motion of the source. This beam is nondiffracting in one dimension: its angular width normal to the direction of motion of the source decreases as 1/d, instead of being constant, so that its cross sectional area increases as d, rather than d2, with the distance d from the source.
Heretofore, these examples of superluminal sources were generated by amplifiers individually driving each polarization device of a radiating source. The large number of amplifiers increases the cost and may adversely affect mean time before failure (MTBF) of such sources.